Kafir limeta

Makrut lime (Citrus hystrix) is native to tropical Southeast Asia. Its fruit and leaves are used in Southeast Asian cuisine, and its essential oil is used in perfumery. In perfumery, the relevant material is petitgrain combava (CAS 91771-50-5), the essential oil obtained from the leaves of the combava, Citrus hystrix. The fruit peel contains a different essential oil, comparable to lime fruit peel oil, whose main components are limonene and β-pinene.

The Plant

C. hystrix is a thorny shrub or small tree, 2 to 11 metres tall, with aromatic and distinctively shaped double leaves. The hourglass-shaped leaves comprise the leaf blade plus a flattened, leaf-like stalk. The fruit is rough and green and ripens to yellow, and it is approximately 4 cm wide. The flowers can have four to five white petals and are fragrant. The fruits have thick skins and taste very acidic and slightly bitter. Both the peel and the pulp contain significant quantities of furanocoumarins.

Names

The plant is called kaffir lime, Thai lime or makrut lime. In Javanese and Malay its names, jêruk purut and limau purut, both mean wart-lime, after the bumpy texture of the fruit. In Réunion Island it is called combava. In South Africa it is usually referred to as Thai lime. Some authors have favored the name makrut lime as more neutral. The most likely origin of the name kaffir lime is the Kaffirs, an ethnic group in Sri Lanka partly descended from enslaved Bantu. In the Philippines the fruit is called kabuyaw or kulubot, and in Vietnam chúc or chanh Thái.

Chemistry and Distinction

The compound responsible for the characteristic aroma of the leaf oil is (S)-citronellal. It makes up to 80 percent of the leaf oil. Citronellal is a monoterpenoid aldehyde with the formula C₁₀H₁₈O and a molar mass of 154.25 g/mol. Citronellal boils at 201 to 207 °C. Steam-distilled leaf oil contained 83.88% citronellal, against 69.88% in the oil of a leaf-twig mixture and 46.47% in twig oil. Leaves store more citronellal than twigs. The leaves are the most promising source of citronellal for industrial applications. Minor components of the leaf oil include citronellol (10 percent), nerol and limonene. Across leaf, twig and mixture oils, minor constituents included linalool (5.24-8.91%), isopulegol (0.47-2.95%), β-citronellol (2.03-12.22%) and citronellyl acetate (4.28-6.48%). A fractional distillation study of an oil from twigs and leaves found at least 20 compounds, five of them main components: β-citronellal (46.40%), L-linalool (13.11%), β-citronellol (11.03%), citronellyl acetate (6.76%) and sabinene (5.91%). In a comparison of four Citrus leaf oils from Malaysia, GC-MS tentatively identified 46 compounds in the C. hystrix oil, and sabinene (3.0%) and citronellol acetate (2.8%) were found only in that oil.

Citronellal is also a main isolate in distilled oils from Cymbopogon plants other than culinary lemongrass, from lemon-scented gum and from lemon-scented teatree. Citronellal has insect repellent properties.

Labelling

Under Commission Regulation (EU) 2023/1545, citronellol and limonene must be indicated in the list of ingredients of a cosmetic product when their concentration exceeds 0.001% in leave-on products or 0.01% in rinse-off products.